Sometimes, I envy first-time cruisers because they experience all the excitement of a cruise from a unique perspective, whereas veteran sailors get accustomed to the quirks of a cruise vacation.
There are a lot of intricacies when planning a cruise compared to a land vacation. For instance, unlike traditional restaurants, dining on a ship usually means set times for meals. Without knowing the difference, you could select a time you're unhappy with.
Posting to the r/CarnivalCruiseFans thread on Reddit, Dangernood69 wrote about their first cruise aboard Carnival Valor, a Conquest Class ship launched in 2004. Though it was an overall positive experience, they made a few "rookie" mistakes and wanted to share them with others.

"We LOVED our cruise. I’m not complaining, just sharing what we learned and were naive [about]," they said, "We are already planning the next one to take our kids on their first trip and will have it booked as soon as we figure out next year’s school calendar in our district."
They chose the wrong dining time

When sailing on a Carnival cruise, you'll have two choices for dining: Anytime or traditional. With the latter, you'll eat at the same time each night, whether 5:30pm or 8:15pm. Additionally, you'll have the same tablemates and wait staff.
Anytime dining is great for those who value flexibility. Rather than scheduling your evening around dinner, you can check in when convenient. Then, you'll be assigned a table on a first-come, first-served basis.
Unfortunately, Dangernood69 wasn't too happy with their selected dining time and recommended choosing Anytime.
Read more: How to change your dining time on a Carnival cruise

"I didn’t know about doing it until too late and we had to do the late time, 8:15. We just don’t like eating late and we ended up only eating in there twice on a 5 day cruise because the late time interfered with the shows we wanted to see," they explained.
"We tried to just go in and get a table maybe someone else didn’t show up for but were sent away and told we could only do that on the last night due to heavy bookings."
On a similar note, Dangernood69 discovered that a lot of food offered in the dining rooms was also in the buffet. This worked in their favor, as they skipped in the dining room and didn't feel like they missed out on much.
Another mistake was purchasing a cheap excursion without doing research

"[W]e cheaped out on a beach excursion in Cozumel and regretted it," Dangernood69 said, "It was $40/person no food included. Who cares right? I’ll pay for food. Then we got there and it was us and literally 500 people lined up on top of each other along the beach with this one little roped off swimming area on the beach."
Though they didn't disclose what beach they went to, they explained that the area was small, and only a couple of dozen people could swim at a time. It was also an extra $5 for an umbrella and $5 for a seat cushion.
"Next time we’ll be going for a much better excursion and paying the money."

For example, Paradise Beach in Cozumel charges $68 for an all-inclusive day pass, which includes drinks, food, Wi-Fi, and access to the club's beach and pool with lounge chairs.
They also warned that itineraries can change. Initally, their cruise aboard Carnival Valor was supposed to visit Costa Maya and Cozumel. However, a few weeks before their sailing, they were informed they'd be visiting Progreso instead of Costa Maya.
Read more: 5 signs your shore excursion is a bad idea
Excursions have restrictions

Something else that surprised Dangernood69 was the weight restrictions on excursions. Many tours came with a limit of 250 pounds.
"I'm not hugely fat but I am 275lbs and could not do the power snorkeling, glass boat, jet ski, etc. I'm not mad about it, I need to lose some weight," they explained.
For example, Carnival's "Power Snorkel, Beach & Pool Adventure" excursion in Cozumel has a strict weight limit of 250 pounds, as well as a minimum age of 8 years old.
They overpacked

Packing for a cruise is different than packing for a regular vacation. As such, it's easy to overpack, erring on the side of caution. However, in Dangernood69's case, they packed too many outfits and ended up wearing swimsuits all day.
"[W]e brought a ton of clothes. Swimsuits and a couple [of] outfits for each day. We ended up in swimsuits literally all day then just getting dressed for dinner. We took more clothes home clean than we dirtied up," they wrote.
However, they didn't bring one item that would have come in handy: a sweatshirt. Because their cruise sailed from New Orleans to Mexico, they assumed it would be warm the entire trip. Once they were out at sea, the evenings got cooler than expected:

"Our first two nights were so cold and windy we couldn’t sit out to watch the movie bc we didn’t come with clothes to be warm."
Read more: 16 Packing Tips for First-Time Cruisers
Dangernood69 didn't understand what prepaid gratuities included

Carnival, like other mainstream cruise lines, requires guests to pay gratuities to tip hardworking crew members. The gratuities cover employees like your cabin steward, dining room servers, the guest services team, and more.
However, other optional purchases have a mandatory service charge, in addition to the ship's gratuities. For example, on Carnival, alcoholic beverages are automatically charged an extra 18%, bringing a $14.00 beverage to $16.52.
Though Dangernood69 prepaid their gratuities, they were taken aback by the service charges, explaining, "[O]n several services there is still a 18% 'service charge' on the receipt. So it feels like you prepay gratuity but then they charge you for it anyways. Especially in the spa. Didn’t matter that I had prepaid gratuity, they hit us with it again."

They also felt as though the gratuity rate was high and would have tipped less had they used cash during their cruise.
Read more: 11 do's and don'ts of cruise ship tipping
They learned soda is available at the bar

On their cruise aboard Carnival Valor, Dangernood69 purchased Carnival's cheapest drink package: Bottomless Bubbles. Unlike CHEERS!, Bottomless Bubbles only includes soda, whereas CHEERS! includes a wider range of drinks from cocktails to glasses of wine, beer, specialty coffee, and more.
Bottomless Bubbles costs $11.21 per day, amounting to roughly $56 on a 5-night cruise, including gratuities. One thing to note about Carnival's drink packages is that if you're sailing from Galveston, New York, or Norfolk, the alcoholic drink package won't activate until the second day due to state laws.
However, guests should expect additional taxes to be charged on embarkation day, as applicable state and local taxes are billed to each guest's onboard account while docked in U.S. waters.

That said, while alcohol is readily available throughout the ship, it took Dangernood69 two days to figure out they could also order soda at the bar.